hyperv: avoid query memleaks on failure

hyperv: avoid query memleaks on failure

The function hypervEnumAndPull consumes query on success, but leaked
it on failure.  Rather than having to change all callers (many of
them indirect callers through the generated
hypervGetMsvmComputerSystemList), it was easier to just guarantee
that the buffer is cleaned on return from the function.

* src/hyperv/hyperv_wmi.c (hypervEnumAndPull): Don't leak query on
failure.

Signed-off-by: Eric Blake <eblake@redhat.com>